We will study the molecular structure of tubulin in crystalline sheets which are induced by small concentrations of zinc ions. Structural information obtained should help in understanding the ways in which tubulin in microtubules and other assemblies carries out its myriad of functions during the development and life of a cell. Electron crystallography, which is ideally suited to the study of twodimensional specimens such as these sheets, will be the main experimental technique. Data from electron micrographs of the crystalline lattice and, where possible, electron diffraction patterns can be combined to yield a three-dimensional density map of the molecule, and this map can then be interpreted in terms of the atomic structure. Electron crystallographic techniques have developed over the last few years to the point where we can make significant contributions using the types of tubulin sheets which have been used in previously published structural studies. We will, though, spend some effort on improving the size and quality of these sheets in order to make extension of this work to high resolution simpler and more efficient.